To prevent transmission of blood borne diseases it has become standard medical practice to use a syringe once, then dispose of it in an acceptable manner. In the industrial world it has been determined that the reuse of a syringe is neither safe nor economical. Consequently, syringes are disposed of daily from such sources as hospitals, clinics, doctors' offices, dentists, and other health care organizations. Since syringes are contaminated with a patient's blood, syringes have the potential to carry with them the diseases of the patient, such as AIDS, Hepatitis, or other dangerous diseases present in a patient's blood. Thus, many unwary health workers and medical waste disposal personnel can be accidentally pricked by these contaminated syringe needles. Unfortunately, contaminated syringes are not always disposed of properly and have been found washed up on beaches or tossed into ordinary trash, where any unfortunate person in proximity of the syringes may be accidentally pricked. Such accidental syringe needle sticks, therefore, create a large health risk not only to healthcare professionals, but also to the general populous.
Another unfortunate consequence of syringe disposal mismanagement is the acquisition and use of syringes by intravenous drug users. Because of the unavailability of new sterile syringes, drug users often reuse the same syringe and needle many times and share the syringe with other drug users. This pattern of syringe use spreads life-threatening diseases throughout the drug using community.
To eliminate the problems of accidental syringe needle sticks, many syringe designs have been created to retract the needle into the body of the syringe after its use. By retracting the needle, the point of the needle is shielded and thus the danger of an accidental prick is removed. Such needle retraction devices are exemplified in U.S. Pat. Nos. 4,955,869 to Bin, 4,643,199 to Jennings, Jr. et al, and 4,507,117 to Vining et al.
To prevent both the problems of accidental needle sticks and repeated use by drug users, many syringe designs have been created whereby the needle is retracted into the syringe barrel and the functionality of the syringe is compromised after a single use. Such syringes may lock the syringe piston in its retracted position, have a breakaway piston shaft, or both, which prevent the syringe's reuse. Such syringe designs are shown in U.S. Pat. Nos. 4,826,484 to Haber et al, 4,790,822 to Haining, 4,747,830 to Gloyer et al, 4,650,468 to Jennings, Jr., 4,562,844 to Carpender et al and 4,026,287 to Haller. All of these references use locking devices that greatly increase the complexity of manufacturing the syringe, thus resulting in syringes that are significantly more expensive than the typical syringe without a safety design.
An alternative safety feature, used to render hypodermic syringes inoperative after one use, is to cant the needle after it is retracted into the syringe barrel. By canting the needle, the needle contacts the inside of the syringe, thus acting as its own safety lock. Such syringe designs are shown in U.S. Pat. Nos. 4,986,813 to Blake, III et al and 4,770,655 to Haber et al. In any event, it is desirable to have such safety features while providing a reliable operating device capable of manufacture at competitive prices.
It is, therefore, an object of the present invention to provide an improved safety hypodermic syringe that selectively renders both the piston shaft and the needle inoperable, and does so in a manner that minimizes both the cost and complexity of manufacturing the syringe.